The object of the present invention is a process for synthesizing methane from hydrogen and carbon monoxide.
It has long been known that methane can be produced with a high selectivity by contacting carbon monoxide and hydrogen with a nickel-based catalyst. This reaction has been more particularly applied, up to now, to the removal of small amounts of carbon monoxide remaining in the hydrogen produced by steam-reforming or partial oxidation of a hydrocarbon fraction.
However, in view of a possible shortage of power resources, the manufacture of methane as a substitute for natural gas has gained interest.
The main difficulty to overcome, when reacting carbon monoxide with hydrogen, is the removal of heat produced by this strongly exothermic conversion.
The conventional use of fixed bed solid catalysts being not favorable to the heat exchange, can lead to local overheatings detrimental to the activity and life time of the catalyst. The process using a heterogeneous catalyst maintained suspended in a non-volatile liquid phase could be applied in that case. This technique has been described, for example, in the U.S. Pat. No. 3,989,734. Although resulting in a better heat exchange, this technique has a lower yield, due to a poorer diffusion of the reactants towards the catalyst, attributable to the presence of the liquid phase.
This explains why it has been proposed, for example in the French Pat. No. 2 374 280, to prepare catalytic systems soluble in an inert liquid medium which can be used thereafter as reaction medium or component of the reaction medium. The homogeneity of the catalyst solution guarantees, on the one hand, a good heat diffusion, thus an efficient removal of the reaction heat, and, on the other hand, a good chemical diffusion, thus a good accessibility of the reatants to the catalyst.
The soluble catalytic system, used in the above French patent, is obtained by admixing and reacting at least one constituent A with at least one constituent B in an inert liquid medium. The constituent A of the catalyst is a nickel compound and the constituent B a reducing aluminum compound.
These catalytic systems have however the disadvantage, when used in a continuous operation, to lose slowly their activity, in the course of time, which results in a high catalyst consumption.